The present study investigated the perception and production of the English consonant clusters of Korean speakers with less complex syllable structure than English, in order to verify the degree of the effects of the first language and markedness in the interlanguage. The data were collected from the perception and production of a large set of stimuli (48 words) by an extensive pool of participants (55 Korean speakers & 6 English speakers as a control group), and the results are analyzed in terms of relative role of first language transfer and markedness effect. Based on the results, important findings were discovered. First, markedness plays an important role in perception, whereas first language does so in production. Second, while in the production of consonant+liquid syllables, both groups make more errors in consonant+/l/ than consonant+/r/ due to the markedness effect, Korean speakers make more errors significantly than English speakers affected by [l]-gemination of Korean.